This invention generally relates to ultrasound imaging, and more particularly relates to penetration of ultrasound waves into a subject being imaged.
The ultrasound wave penetration of current day diagnostic ultrasound machines when performing color flow imaging is compromised by FDA regulation. The FDA regulates the acoustic power output from diagnostic ultrasound imaging machines to avoid the possibility of undesirable effects in the body due to cavitation and heating. These effects are regulated by means of limits on MI (Mechanical Index), and ISPTA (Intensity Spatial Peak Temporal (time) Average), respectively. Ultrasound waves typically are applied to a subject by holding the face of a transducer against the skin of the subject. The temperature of the transducer face is limited for safety. When performing color flow imaging, an ultrasound imaging system typically reaches the ISPTA and probe temperature limits before reaching the MI limits. As a result, the system limits the transmit current to a level much lower than would be required to avoid the MI limit. The current limitation compromises the system's ability to image deep vessels where the limited transmit signal is highly attenuated.
A primary method used to improve penetration is to increase the number of firings (transmit & receive) in the same direction and perform some type of averaging across these firings. The primary disadvantage to this approach is the resulting decrease in the frame rate of the display, thereby degrading temporal resolution.